Tubing



July 5, 1966 P. GRASME TUBING Filed April 17, 1964 Fly. 5 l /0R ART United States Patent "Ice 3,259,109 TUBING Paul Grasme, Berlin-Spandau, Germany, assignor to Licentia Patent-Verwaltungs-G.m.b.H., Frankfurt am Main, Germany Filed Apr. 17, 1964, 'Ser. No. 360,634 Claims priority, applicatign 6(germany, Apr. 18, 1963,

7 Claims. 61. 122-235 The present invention relates to tubing, and, more particularly, to a pre-formed curved tubular piece for use in meander-shaped composite tubing which itself is used in conjunction with the surfaces in boilers.

The heating surfaces in the combustion chamber as well as in the actual heating chamber of forced-circulation boilers used with refining furnaces are frequency constituted by meander-shaped tubes. The tubes lie close to each other in the combustion chamber or firing box and, in order to prevent the liquid slag from coming into contact with the material in which the tubes are embedded, the latter are additionally provided with spikes or pins and are lined with tamped material. In the case of conventional tubing, however, it has been found, particularly between the bends of the tubing in the course of the meandering as well as at the places where several tube sections come together, that large surface areas of the heating surfaces will remain uncovered by tubing. Despite the fact that these interspaces are provided with spikes and tamped material, not enough heat flows to the tubing, through which water flows, so that the tamped mass melts away and the spikes burn out. As a result, the liquid slag comes into contact with the refractory brickwork of the furnace. This is bad because the liquid slag reacts chemically with the heat-resistance brickwork so that the latter is soon destroyed.

In the case of firing chambers for boilers with dry ash removal, flue ashes and particles of coke which are carried along will come to be deposited in the interspaces left uncovered by tubing, where these particles become sintered in place and form points at which slag may become encrusted on the heating surfaces. The same thing also happens frequently in the actual heating chamber of coalheated boilers in which the flue gases are at a high temperature. In the case of oil burning boilers, flue gases containing S0 and 80;, will come into contact with the refractory lining of the combustion and heating chambers, and this, too, attacks the lining chemically and ultimately destroys the same.

It has previously been attempted to overcome the above drawbacks by lining the interspaces between the bends of the tubing and the space between the tube sections at points where a number of them come together, by means of sheets which are welded to the hollow bends. It has been found, however, that, due to the high temperature and to the insuflicient transfer of heat to the tubes, the sheets will very soon burn through to a large extent.

It is, therefore, the primary object of the present invention to provide a way in which the above-described drawbacks are overcome and this, according to the present invention, is accomplished by letting the tubular connecting pieces which are in the shape of curved sections and which, at each end region, are of generally circular cross section, have a flat elliptical cross section in the region of maximum curvature, generally the middle of the section. The transition of the cross section of the curved tube section, from end region to region of maximum curvature to end region, is continuous. Thus, with the major axis of the elliptical cross section extending in the plane in which the tube section curves, the interspaces between the meandering tubing and the places at which a 3,259,109 Patented July 5, 1966 number of tube sections come together, will be filled out. More particularly, the tube sections are disposed uniformly on the heating surface of the boiler with which the tubing associated, the size of the curved tube sections being such that the uncovered portion of the heating surface is maintained substantially constant between straight and bentportions of the tubing so as to provide uniform cooling of the heating surface.

Additional objects and advantages of the present invention will become apparent upon consideration of the following description when taken in conjunction with the accompanying drawings in which:

FIGURE 1 shows one embodiment of a tube section according to the present invention.

FIGURE 2 is a sectional view taken on line 22 of FIGURE 1.

FIGURE 3 shows another embodiment of a tube section according to the present invention.

FIGURE 4 is a sectional view taken on line 4-4 of FIGURE 3.

FIGURE 5 shows the arrangement of tubing incorporating curved tube sections according to the present invention, this tubing being shown as positioned on a heating surface of a boiler.

FIGURE 6 shows a similar arrangement of tubing which is constructed according to the prior art, i.e., the tubing shown in FIGURE 6 lacks the curved tube section according to the present invention.

Referring now to the drawings and to FIGURES 1 and 2 thereof in particular, the same show a curved tube section 10 which is constituted by two pre-formed shells 10a and 10b, the same being welded to each other, as shown at 12, to form the complete tube section. The tube section has, at each of its end regions a, a generally circular cross section, whereat the tube section is welded, as shown at 22, to another tube section 20 which has a similarly configured end region but which may extend, throughout its length, in any manner to give the tubing as a whole the desired meandering path.

The tube section 10 is shown as having, in approximately its middle, a region of maximum curvature b, which, as best shown in FIGURE 2, is .of substantially elliptical cross section. The major axis m of the elliptical cross section extends in the plane in which the tube section curves, i.e., the plane of the drawing of FIGURE 1. The transition of the cross section, from end region a to region of maximum curvature b to end region a, is continuous.

In order to impart the tubing its desired predetermined rigidity, each of the shells 10a, 10b, has a wall thickness which, when the shells are welded together to form the complete tube section, imparts this predetermined rigidity to the complete tube section.

In order that the water or other fluid flowing through the tubing of which the curved tube section is a part will.

flow therethrough at a substantially constant rate, the internal cross sectional area of this tube section is maintained substantially constant throughout the entire length of the tube section.

In the embodiment of FIGURES 3 and 4, the curved tube section is made up of shells 100a and 100b, welded together by welds 112, the shell 100b being provided with an an integral fin 101 which extends, generally, in the direction of the major axis m of the elliptical cross section. In this way, coverage is provided for the wall surface area immediately adjacent to the wall surface covered by the hollow tubing proper.

FIGURE 5 shows meander-shaped tubing which, in accordance with the present invention, includes curved tube sections of the type shown in FIGURES 1 through 4, while FIGURE 6 shows meander-shaped tubing 200 which lacks the tube sections according to the present invention. The meander-shaped tubing is, in each case, illustrated as being positioned over the heating surface H of a boiler. It will be appreciated from a comparison of FIGURES 5 and 6 that the tubing incorporating the sections according to the present invention provides a substantially complete coverage of all portions of the heating surface, even at a place where several tube sections come together, while the uncovered portion of the heating surface is maintained substantially constant between straight and bent portions of the tubing, which itself is disposed uniformly on the heating surface, so as to provide uniform cooling of the heating surface.

It will be understood that the above description of the present invention is susceptible to various modifications, changes, and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

What is claimed is:

1..In combination: a boiler having a heating surface; and meander-shaped tubing associated with said heating surface, said tubing incorporating a plurality of tube sections, at least some of said tube sections being curved, each of said curved tube sections having, at each end region, a generally circular cross section and, at its region of maximum curvature, a flat ellipitical cross section, the major axis of said elliptical cross section extending in the plane in which the respective tube section curves, the transition of the cross section of each tube section, from end region to region of maximum curvature to end region, being continuous, said tube sections being disposed uniformly on said heating surface and the size of said curved tube sections being such that the uncovered portion of said heating surface is maintained substantially constant between straight and bent portions of said tubing so as to provide uniform cooling of said heating surface.

2. The combination defined in claim 1, further having,

in said region of maximum curvature, fin means extending generally in the direction of the major axis of said elliptical cross section, thereby to provide coverage for the wall surface area immediately adjacent the wall surface covered by the tubing proper.

3. The combination defined in claim 1 wherein said tube section comprises two shells and weld means joining said shells to each other, thereby to form the complete tube section.

4. The combination defined in claim 3, further having fin'means integral with one of said two shells, said fin means extending generally in the direction of the major axis of said elliptical cross section, thereby to provide coverage for the wall surface area immediately adjacent the wall surface covered by the tubing proper.

5. The combination defined in claim 3 and having a predetermined rigidity, said shells each having a wall thickness which, when said shells are joined together by said weld means to form the complete tube section, imparts said predetermined rigidity to the complete tube section.

6. The combination defined in claim 1 wherein said region of maximum curvature is located generally in the middle of the tube section.

7. The combination defined in claim 1 wherein the internal cross-sectional area of said tube section is substan tially constant throughout the entire length of the tube section, in consequence of which a fluid may flow through said tube section at a substantially constant rate.

References Cited by the Examiner UNITED STATES PATENTS 2,170,342 8/1939 Bailey 122448 3 2,562,442 7/1951 Attschuler et al 122250 3,129,698 4/1964 Davis 122-510 KENNETH W. SPRAGUE, Primary Examiner. 

1. IN COMBINATION: A BOILER HAVING A HEATING SURFACE; AND MEANDER-SHAPED TUBING ASSOCIATED WITH SAID HEATING SURFACE, SAID TUBING INCORPORATING A PLURALITY OF TUBE SECTIONS, AT LEAST SOME OF SAID TUBE SECTIONS BEING CURVED, EACH OF SAID CURVED TUBE SECTIONS HAVING, AT EACH END REGION, A GENERALLY CIRCULAR CROSS SECTION AND, AT ITS REGION OF MAXIMUM CURVATURE, A FLAP ELLIPTICAL CROSS SECTION, THE MAJOR AXIS OF SAID ELLIPTICAL CROSS SECTION EXTENDING IN THE PLANE IN WHICH THE RESPECTIVE TUBE SECTION CURVES, THE TRANSITION OF THE CROSS SECTION TUBE SECTION, FROM 